1. Field of the Invention
The present invention relates to a system and method for converting into useful energy movements imparted thereto by the movement of water, preferably sea waves and/or sea currents.
The present invention also relates to a power generation system which extracts useful power from water waves. In particular, the invention relates to the interaction of various elements of the design of a wave driven generator unit. More specifically, the present invention absorbs wave energy, converts that energy into electrical energy, and transports that electrical energy from its offshore point of generation to a land-based power grid. Thus, the present invention produces large quantities of power economically for a public utility or large industrial user.
Further, the present invention also relates to a system utilizing wave engines and more particularly wave engines used to drive electric generators (i.e., Pelton Wheels) or linear inductance generators, wherein wave driven generators use a plurality of different sized floats to present a black body to the incoming wave energy whereby wave energy is nonlinearly coupled into hydraulic pumping means.
2. Background of the Prior Art
Various forms of apparatus are known having a movable member which is moved by sea waves relative to a fixed structure and whose movement is converted to usable energy. The fixed structure is usually mounted on the sea bed and this produces vast engineering problems and difficulties. It also means that such apparatus cannot be used in great depths of water. The known apparatus usually can only extract energy from one direction of water, i.e. either horizontal movement or vertical movement but not both. This greatly reduces the efficiency of the apparatus.
It has been well known for many years to harness wave energy by means of apparatus comprising two or more rafts or floats connected together so as to be pivotally movable relative to one another. Wave action causes the relative pivotal movement, and the relative movement is converted into useful energy.
Also, it has long been known in the art of power generation to use the potential energy available in ocean waves to lift a float. A variety of ingenious mechanical linkages have been developed in an attempt to efficiently capture the energy of ocean waves. See, for example, U.S. Pat. Nos. 562,317; 632,139; 694,242; 738,996; 886,883; 917,411 and 986,629. All of these early patents rely upon mechanical linkages between fixed floats to trap the rocking, lifting, falling or longitudinal motions of waves. All of the engines disclosed in these patents are mechanically complex and highly inefficient.
While all the above cited references depend on the potential energy of waves to develop motive power, some wave motors in the past taught the use of the wave's kinetic energy, such as U.S. Pat. No. 1,072,272. A careful study of the prior art shows that most historical wave motors utilize either (1) the kinetic energy of waves by devices such as paddle wheels, or (2) the wave's potential energy by a float or a series of floats. Few devices utilize both forms of energy. The prior art, insofar as it relates to wave engines that rely upon the lifting power of waves, i.e., its potential energy, rely either on a single float, for example U.S. Pat. Nos. 1,202,742; 1,471,222; 1,647,025; 1,746,613; 1,953,285 and 1,962,047, or utilize a series of floats of the same size, for example U.S. Pat. Nos. 1,925,742; 1,867,780; 1,688,032; 1,567,470, and 1,408,094. Additionally, many early wave motors are extremely complex mechanically. For example, see U.S. Pat. Nos. 1,528,165; 1,169,356 and 1,818,066.
Many prior art wave motors teach the direct linear coupling of the float's motion through either mechanical or hydraulic means to the motion of a shaft or piston. As a result, such wave motors had to be very rugged and heavy to withstand the wide spectrum of wave energy incident upon them. For example, one wave motor installed in Atlantic City, N.J. consisted of six foot cylinder floats 4 feet high. Each float weighed about 3,100 pounds and was lifted two feet by waves 11 times per minute. They drove a horizontal shaft by means of chains and rachets, developing about 11 horsepower, steadiness being obtained by the use of heavy flywheels. The inefficiency, capital cost and complexity of such prior art wave motors caused them to be unsuccessful. (Power, Jan. 17, 1911). (A similar wave motor was proposed by Smith in Mechanical Engineering, September 1927 at page 995.)
The most modern wave motors taught by the prior art do not differ significantly in the manner of operation from wave engines taught at the beginning of this century. See, for example, U.S. Pat. No. 3,879,950, issued Apr. 29, 1975 to Kiichi Yamada for a wave generator to be used in conjunction with an offshore nuclear power plant. This modern wave motor uses a plurality of identical floats whose motion is coupled linearly to a series of pneumatic pistons. Unfortunately, such a linearly coupled collector cannot efficiently trap wave energy.
Waves in the ocean vary in amplitude, or wave height, from a fraction of a foot to over 50 feet and in frequency from a wave length of less than 5 feet to over 1,000 feet. To extract the maximum potential energy from any given wave, a float must be capable of dynamically coupling to the wave's movement. A given size float will respond most efficiently to only one wave length. To be efficient, a wave motor must provide a plurality of different size floats capable of coupling efficiently into a broad spectrum of differing wavelengths, i.e., to all the waves from which power must be efficiently extracted. Broadly, this concept is called “resonance”.
In addition to resonance with a broad spectrum of wavelengths, the floats of an efficient wave motor must be capable of extracting power from both low and high amplitude waves. Because waves differ in amplitude by as much as two orders of magnitude, any device that extracts power by linearly coupling wave movement to gears or pistons will have to be inefficient in extracting power from either the high or low amplitude end of the wave power spectrum.
Theoretically, a single float acting alone, even if it is the proper size, can only absorb a fraction of the available power from a wave incident upon it. This is caused by the fact that a portion of the wave's energy is absorbed by the float, another portion is reflected back from the float and another portion is transmitted through the float to its attached structures. This fact, as well as the fact that wave motors taught by the prior art do not couple efficiently into either the frequency or amplitude spectrum of ocean waves, have caused all prior art wave motors to be very inefficient.
Methods and apparatus designed to capture and convert wave energy into a variety of other forms of useful energy are described in a number of prior art publications and patents, as noted above. These early patents relied on mechanical linkages between fixed floats to trap the rocking, lifting, falling, or longitudinal motion of the waves but were highly inefficient due to their mechanical complexities. Some of the most mechanically complex devices are illustrated in U.S. Pat. Nos. 1,169,356, 1,471,222, 1,528,165, 1,818,066.
The U.K. Patent Application No. 2113311A discloses a particular arrangement of rafts or floats, namely two rafts connected to one another for relative pivotal movement about a common pivotal shaft, and a damping mechanism for damping the movement of the pivotal shaft so as to maintain the pivotal shaft substantially fixed relative to the mean level of the water. The relative motion of the rafts drives pumps, which drive seawater to an elevated storage tank from which the water may be released to generate electricity.
In prior art wave powered prime movers such as described in U.S. Pat. No. 4,098,084 (Cockerell), the pontoons or buoyant members, will in certain long wave conditions, i.e. when wave length is greater than four times the length of an individual pontoon, become wave followers and thus will not move relative to each other to any great extent. A study of the prior art shows that most inventions designed to convert wave energy into useful energy utilize either (1) the kinetic energy of the waves by devices such as paddle wheels, or (2) the wave's potential energy by a float or a series of floats. The vast majority of prior art inventions for converting wave energy into useful energy rely upon the potential energy of a wave, i.e., the lifting power of the wave. Many such inventions rely upon a single float for absorbing a wave's energy. See, for example, U.S. Pat. Nos. 562,317, 738,996, 1,202,742, 1,471,222, 1,647,025, 1,746,613, 1,953,285, 1,962,047, and 3,487,228. Other early inventions rely upon a series of floats for converting the wave's potential energy into other forms, examples of which include U.S. Pat. Nos. 632,139, 855,258, 882,883, 917,411, 1,408,094, 1,567,470, 1,688,032, 1,867,780, and 1,925,742.
U.S. Pat. No. Re31,111 relates to wave driven generators comprising a plurality of floats that are tuned to be responsive to incoming waves by the use of different sized floats whereby wave energy is extracted by the floats and converted into hydraulic energy. This hydraulic energy is then employed to drive a turbine generator and generate electricity. The floats are connected together by hinges as to form what is defined as a “Hagen-array”. Each float is pivotally connected to a larger float in such a manner as to allow relative movement between the floats. Hydraulic pistons and cylinders are mounted between the floats. These hydraulic pistons and cylinders are responsive to the relative movement between the hinged floats, and generate hydraulic energy in response to such movement. This hydraulic energy is stored in an accumulator which is then converted into electrical energy by a turbine-generator, located onboard of one of the floats. The array is moored to the sea floor by cables in a manner such that it is free to rotate so the floats maintain a desired position, i.e. facing the incoming waves.
A conceptual presentation of a wave energy conversion system appears in Transactions of the ASME, page 492, Vol. 105, December 1984. The system depicted therein includes an array, composed of rafts or floats of various lengths hinged together, and hydraulic pistons and cylinders positioned between the floats for absorbing wave energy and converting it into electrical energy. An articulated raft system, or array, is shown moored to the sea floor by a single anchor leg mooring system. A schematic representation of an onboard power conversion system is illustrated with the components of the system including hydraulic pistons and cylinders, accumulators, turbines, and generators. A submarine cable is illustrated for transmitting the electrical energy that is generated.
The Hagen-array system of hinged rafts suffers from the fact that the unit length of the rafts perpendicular to the crests (parallel to the line of incidence) must be approximately one wave length of the incident waves. The result is good efficiency relative to the beam dimension of the rafts but poor efficiency in terms of energy extracted per raft size or weight. The poor efficiency results because the Hagen-array system does not make use of the physical parameters of the rafts other than unit length to tune the system properly so as to respond to the broad spectrum of wave frequencies that occur in the ocean.
A number of other patents disclose utilizing a plurality of floats to convert wave energy into useful energy. For example U.S. Pat. Nos. 4,392,349, 4,098,084, 3,879,950, and 1,408,094 disclose raft-like floats, hinged together, so as to form articulated chains or arrays. U.S. Pat. Nos. 4,241,579, 4,073,142, 4,048,801, 1,757,166 disclose energy conversion systems where a plurality of buoy-like floats are positioned in particular patterns so that wave energy resulting in upward and downward reciprocation of the floats is converted into useful energy. U.S. Pat. No. 3,758,788 discloses an energy conversion system where buoyant structures are connected together by pivotal structures and bellows which are activated by movement between the buoyant structures. The positive air or fluid pressure is then used to drive a turbine generator to generate electrical energy. A variety of hinges are disclosed for connecting rafts or floats together. For example, see U.S. Pat. Nos. 4,098,084, 3,879,950, 1,408,094, 917,411, 882,883, and 632,139. Additionally, U.S. Pat. No. 4,118,932 discloses hinging two floats together whereby the hinge also forms a pump which generates hydraulic energy in response to the relative rotational movement of the floats about the hingeline. Other prior art patents disclose a variety of pistons or bellows to convert wave energy into hydraulic energy, such as U.S. Pat. Nos. 4,408,454, 4,208,875, 4,013,382, 3,879,950, 1,757,166. Additionally, the device known as the Salter “nodding duck” which is disclosed in U.S. Pat. No. 3,928,967 utilizes a variable stroke rotary pump to convert the pivotal motion of its energy removing member into usable hydraulic energy.
U.S. Pat. No. 3,928,967 describes a system composed of a plurality of wave power absorbers deployed so as to intercept power from a line parallel to the incident wave crests that is long compared to the dimension perpendicular to the wave crests. The device described in this patent is an efficient absorber but suffers from the lack of stable reference necessary for power extraction. Although the device incorporates several features that improve the efficiency of energy capture, the concept fails to incorporate the more important features necessary for economical wave energy generation efficiency.
A number of other mooring or anchoring means are disclosed in the prior art. See, for example, U.S. Pat. Nos. 4,408,454; 4,013,382; 3,879,950; 1,746,613; 917,411 and 855,258. The supporting structure or mooring system required to operate many of these inventions, however, is quite elaborate and costly. See, for example, U.S. Pat. Nos. 1,757,166; 3,879,950; 3,928,967 and 4,013,382. A number of prior art patents disclose converting the captured wave energy into electrical energy. See for example, U.S. Pat. Nos. 4,152,895; 4,013,382; 3,879,950; 3,487,228; 1,962,047; 1,757,166 and 738,996.
U.S. Pat. No. 1,757,166 covers an apparatus and method of obtaining power from ocean waves. However, even this prior art teaches the use of a plurality of single unconnected floats of the same size. No prior art found by the inventor teaches the advantages of tying together a group of floats in an array to form a wave trap to capture reflected and transmitted wave energy. Also, no prior art found by the inventor teaches the nonlinear coupling of the floats to their associated power extraction devices.
The prior art is limited either to the mechanism by which power is transferred from wave to floating structure or to methods of converting the motion of a floating structure to useful power. The prior art does not make allowance for the random character of the incident waves by matching floating structure response to wave conditions that vary (1) annually for different locations around the world, (2) monthly (seasonal) fluctuations, and (3) over short intervals of time varying from fractions of an incident wave period to over several wave periods. Further, the prior art does not match the power train impedance to the incident wave characteristics so as to optimize power absorption and short time energy storage to achieve maximum power train efficiency.
The prior art does not analyze the economic factors that must be considered for an energy system to provide base load power to a shore installation. For example, the selection of deployment site includes factors such as bathymetry conditions for mooring and power transmission, distance from shore, matching onboard power generation to shore side power grid specifications, mooring depth, power collection from individual wave energy generating units, and power conditioning and transmission to shore.